I. Field of the Invention
This invention relates generally to a mechanical latch for securing a door or lid to a container. More specifically, this invention relates to a vacuum actuated mechanical latch, which latches the door to the container, retaining the door in a hermetically sealed position. Jarring or bumping the container will not disengage or release the latch from the container.
II. Discussion of the Related Art
The sensitivity to contamination of materials used to produce semiconductors is a significant problem faced by semiconductor manufacturers. Standardized Mechanical Interface (SMIF) systems have been designed to reduce contamination from airborne particles and vapors during the processing, transportation or storage of these sensitive materials. A SMIF system includes a hermetically sealable container used to transport a semiconductor substrate made from the sensitive materials. A SMIF cassette is typically used to confine the semiconductor substrate within the SMIF container. The semiconductor substrate may include a wafer, LCD, flat panel display, and or memory disks. For discussion purposes, and without limitation, reference will be made to semiconductor wafers.
During the processing, transportation and storage of semiconductor wafers, it is critical that the semiconductor wafers be isolated from damaging particulate. The size of the particulate that is damaging to the semiconductor wafer is determined by the geometry of the semiconductor. As the geometry of the semiconductor decreases, the size of the particulate to be eliminated likewise decreases. The presence of vapors or static discharge in the environment also impairs the production of semiconductors, including the wafers themselves. Hence, use of materials having low outgassing characteristics is desired.
It has been found that slight abrasions to the SMIF system containing semiconductor wafers can generate damaging particulate. Static electricity may attract the abraded damaging particulate to the inside surfaces of the SMIF container or to the semiconductor wafers themselves. When particulate has attracted to the inner surface of the SMIF container, moving the container may cause particulate to become airborne, landing on the semiconductor wafers and later damaging the semiconductor wafers. Circulating and filtering air or other gas within the SMIF container does not readily remove the particulate from the inner surfaces of the SMIF container. Although the SMIF container may be cleaned, it is difficult to clean the container entirely of particulate attracted to the inner surface of the container.
The maintenance of an adequately clean environment during the transportation, processing and storage of semiconductor wafers is crucial. Automated processing equipment has been developed to minimize contact and exposure of the semiconductor wafers to damaging particulate. Likewise, containers or isolation structures have developed which protect the wafers and can be manipulated robotically by the processing equipment. Typically, the isolation structure or SMIF container is hermetically sealed from the external environment by a door or lid and is opened only when engaged in a clean mini-environment by the port door of a processing tool. In this way, risk of contamination is substantially reduced. Thus, it is important that the door of the SMIF container remain hermetically sealed, unless disengaged by the processing equipment in a clean environment.
Once a hermetic seal is formed, the door must remain secured to the container. Various latching arrangements have been developed to secure the door to the container, while minimizing the amount of mechanical movement and particulate generation. One such device is disclosed by Gallagher et al., in U.S. Pat. No. 5,291,923 (the '923 patent). This patent discloses a flexible, collapsible, membrane or bladder type seal. A vacuum is applied through a manifold to the interior of a closure member used to seal a SMIF container. When the vacuum is applied, the seal collapses thereby allowing the door to be removed. When the vacuum is released, the seal slowly expands to its original shape. To decrease the amount of time it takes for the seal to expand to its original shape and seal the door to the container, a positive pressure may be applied.
The arrangement disclosed by Gallagher et al. has proven to be effective in various circumstances. However, severe bumping or jarring can cause the door to disengage from the container, contaminating the semiconductor wafers stored within the container. Such bumping and jarring occurs all too often in the typical manufacturing facility. Also, the vacuum arrangement increases the necessary time for the processing equipment to release or engage the door to the container. Hence, a need exists for a latching member that may be engaged or disengaged quickly, that is not as easily disengaged by jarring or bumping.
Various mechanical latches, such as that disclosed by Parikh et al. in U.S. Pat. No. 4,724,874 have been used with some success. However, efforts to design such latches to eliminate the generation of particulate when the latch is engaged and disengaged have been unsuccessful. As mentioned above, any amount of particulate generated may be damaging to the semiconductor wafers.
Hence, a need exists for a latch which, among other things: (1) may be engaged and disengaged efficiently by processing equipment; (2) is not easily overcome by bumping or jarring the container; (3) minimizes generation of contaminating particulate during actuation of the latch; and (4) isolates and removes particles abraded from the latch so such particles do not contaminate the contents of the container. The present invention provides such a latch.